“Black” and “white” twins

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Update: More comments here, here and here.
End update

Desidancer and Diana both pointed me to this story about a mixed race couple who gave birth to daughters of very different phenotypes. The explanation in the story is about right, the loci which give you a gestalt impression of racial identity are a tiny sample of your overall genome. In the story it is reported that 7 genes control skin color and F1 (first generation) hybrids should carry half of the variants of each race (since their parents contribute exactly 50% of the genes to each). But the F2 generation can come out as a range of combinations, so it stands to reason that mixed-race couples will have children who vary a great deal in phenotype as the alleles resegregate themselves into alternative combinations. I lay out the details in By the Punnett Square. South Asians, who often exhibit a wide range of color variation from near white to near black, should not be surprised at this sort of dynamic, as the variance within a family can be rather large in complexion.

In any case, independent assortment implies that even if the coloration of these two children reflects one of their ancestral ethnic groups, other traits do not necessarily line up in such a fashion. Since the twins above are babies it is hard to discern facial traits (they just look like babies), but I wouldn’t be surprised if the “white” and “black” baby had facial traits that were more equidistant to the metrics of whites and blacks (this would be expectation, though you expect a lot of variance still). There is a reason that in much of the southern part of the New World where admixture between Africans, Europeans and American indigenes is common, there are dozens of definitions for racial phenotypes, because the full range of appearance is expressed in a large enough mixing population (eg, there are terms for people with Negroid facial features and hair form and Nordic coloration and European facial features and hair form and Sub-Saharan African coloration).

By the way, as personal stories like this become more common hopefully we’ll stop hearing about how everyone in the future will be brown because of admixture. More values at each variable will result in an increase in variance for the distribution, not a decrease.

Update: OK, I think I need to repost this link, The incidence of superfecundation and of double paternity in the general population:

Sometimes superfecundation occurs by two different men. The frequency with which this occurs must depend on rates of infidelity (promiscuity). It is suggested that among DZ twins born to married white women in the U.S., about one pair in 400 is bipaternal. The incidence may be substantially higher in small selected groups of dizygotic twin maternities, eg. those of women engaged in prostitution.

In other words, double paternity is a possible explanation, but if the number of loci in question is seven or less than this is surely will the expected range due to variance emerging from heterozygosity in the parents1 (and we are only looking at skin color here from what I can tell, the two infants are still of the “baby race,” other features are not at play). I don’t think that the expectation of double paternity, evening adjusting for SES, approaches the probability that “white” and “black” color genes will resegregate in this fashion.

Update II: David points out that this is being reported in the British newspapers, which does alter your Bayesian priors, but walk around Lowell, Massachusetts, and observe the range in phenotype of the Cape Verdian community. The general point still stands.

1 – Fisher’s 1918 paper dealt in large part with the variance expected from heterozygous parents.

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37 Comments

  1. I’d still want a paternity test if I were dad. That’s probably at least as likely an explanation.

  2. That’s probably at least as likely an explanation. 
     
    not really. link
     
     
    It is estimated that at least one dizygotic (DZ) twin maternity in twelve is preceded by superfecundation (the fertilization of two ova by sperm from different coitions). Presumably this parameter varies from population to population eg. with coital rates and rates of double ovulation. Sometimes superfecundation occurs by two different men. The frequency with which this occurs must depend on rates of infidelity (promiscuity). It is suggested that among DZ twins born to married white women in the U.S., about one pair in 400 is bipaternal. The incidence may be substantially higher in small selected groups of dizygotic twin maternities, eg. those of women engaged in prostitution. 
     
     
    even if this woman has a greater than 1 in 400 chance of bipaternality because of socieconomic parameters, i don’t think it reaches the same probability as one twin coming out “white” and another “black.” depending on the # of loci that is lower than 1 out of 100 i think for first generation hybrids (the children will converge in phenotype as they look like humans insteads of babies and other features aside from skin color become salient in determining ethnic heritage). 
     
    p.s.: i hope it goes without saying that the probability of either child coming out the color they are is they share the same father and he is white or black is trivial. if matthew is suggesting that “white baby” baby has white father, but so does black baby, well, “dominance” don’t work that way bro.

  3. Hmm, I would still say ‘Cherchez le milkman’.

  4. …also, as this is a story in a British tabloid, which pays good money for ‘human interest’ stories, I think that affects the Bayesian priors! Sorry to be so cynical, but the kid on the right is so white she must glow in the dark (not to mention the golden hair and blue eyes). I wonder if partial alibinism is a possibility?

  5. I think that affects the Bayesian priors! 
     
    ok, that got my attention :) i forgot my maxim to beware of british newspapers!

  6. Don’t you see this sort of occurence all the time in places like Afghan Central Asia & Iran – two swarthy parents with both typical & fair, euro-looking offspring? Even eastern europe and the middle east sometimes produces this kind of thing. 
     
    As they grow older and their features develop, you may see more similarities appearing.

  7. David B, 
     
    I agree the “White” baby looks almost Albino to me?! 
     
    Also, the “White” seems to have a narrower face than the “Brown” baby, perhaps due to bipaternality?!

  8. It’s not uncommon to see lightly pigmented babies start to darken for up to 2 years after birth. Granted, if the lighter child’s eyes and hair start to change she probably won’t match the coloring of her sister. Nevertheless, this is an interesting case.

  9. In fact, among some south Asians i knew, one of the sibs was basically tamil-like in features & complex., while the other was almost redheaded, had green eyes & fair skin, and was of a generally northern indian style appearance. The parents weren’t nearly as varied as the offspring were, as i recall. 
     
    Puerto Ricans/Guyanese/Trinis & other West Indians have been susceptible to this, too. 
     
    I suppose all this has to do with allele assortation, no?

  10.  
    I suppose all this has to do with allele assortation, no?
     
     
    yes. my mother and her siblings range from dark brown to olive in complexion.

  11. Maybe they’re one of the families in UK edition of the series “Black and White” on the FX newtwork.  
     
    ;-)

  12. Actually they both look rican.

  13. An interesting case, and cute babies, but I’m rather more concerned about the fact that a 19-year-old and a 17-year-old are parents of twins. Dole, anyone?

  14. The referenced article states that both babies were born with blue eyes and the color turned to brown for one with darker skin. Wouldn’t that suggest one father for both babies?

  15. Will some people predict these sisters as adults will show a gap in performance due to racism?

  16. Will some people predict these sisters as adults will show a gap in performance due to racism? 
     
    if racism, or social pressures of any sort coupled with phenotype, are effective, then they should, shouldn’t they? i had two close friends who were half south asian and have irish. one looked white, while the other was assumed to be middle eastern or latin american. the white one has basically assimilated to a white identity (he goes by “sean,” not his muslim name) while the other is more brown in culture and more orthodoxly muslim.

  17. Years ago I worked with a Brazilian PhD student from a family which was according to the photos of family assemblies very multicolored, even including a grandfather of German origin, who moved to Brazil around 1945 ;-). 
     
    She said that in her family when a new child would be expected, they made bets on the sex AND color. She herself looked a bit Gypsy, with big waves in her hair (not nappy). Her sister looked very European. However, with her a bit darker husband, they did have one rather dark negroid and one fair daughter. Ther student mentioned that there WAS some discussion about the darker daughter between her sis and her hubby.

  18. To explain my cryptic comment about Bayesian priors, my point was that the source of this report is a British tabloid which pays for stories. The kind of people who sell stories to tabloids tend to be pretty low-rent (think Jerry Springer). In this case, as someone has pointed out, the parents are 19 (the mother) and 17 (the father) (which means they must have been about 17 and 15 when the babies were conceived). This must substantially raise the prior probability of multiple paternity, as compared with the probability in the general population. I would guess it might be as high as 1 in 20. 17-year-old girls who sleep with 15-year-old boys probably aren’t very choosy. (OK, he *may* be her one true love, but I wouldn’t bet on it.) 
     
    I would identify the posible explanations for the difference between the babies as follows: 
     
    1) random Mendelian segregation, as explained by Razib in his post 
     
    2) the babies have different fathers 
     
    3) the ‘white’ baby is a partial albino of some kind 
     
    4) the whole story is a scam, and the babies are not even siblings. One or both of them might have been ‘borrowed’ to produce the story. The Daily Mail is reputable enough not to have invented the story itself, but it might have been conned by the ‘parents’, probably under the guidance of some older person.

  19. the little brown one looks a lot like dad. 
     
    “” The odds against of a mixed race couple having twins of dramatically different colour are a million to one.” 
     
    How do they figure this’n out?

  20. Obviously two different fathers. Wanna bet real money?

  21. The odds against of a mixed race couple having twins of dramatically different colour are a million to one. 
     
    from the artice: 
     
    For a mixed-race couple, the odds of either of these scenarios is around 100 to one. But both scenarios can occur at the same time if the woman conceives non-identical twins, another 100 to one chance. 
     
    This involves two eggs being fertilised by two sperm at the same time, which also has odds of around 100 to one.
     
     
    i think the last two steps are conflated, i don’t get what they are trying to say here, as non-identical twins implies two eggs being fertilized, right? unless you believe in half-twins or something. i think a clearer way would be to state 
     
    (probability of white sibling & black siblings)*(probably of siblings being dizygotic twins) 
     
    you can calculate the expected probability that two siblings from two mixed race parents would come out this way. that is, imagine 1000 mixed race couples at 2 children each, a subset of the 1000 sib pairs will look something like that. you don’t stipulate how you get the 2 children, so a subset of the 1000 sib pairs will be dizygotic twins. the two probabilities are independent, so such multiply them out once you have the numbers empirically (you can calculate the expected sib pair frequencies if you know the genetic architecture a priori).

  22. Even though an underage black couple living in a very promiscuous country is probably the most likely candidate for a superfecundation, I incline towards the third hypothesis, that is, pure British tabloid bullshit.

  23. “Since the twins above are babies it is hard to discern facial traits (they just look like babies)” 
     
    This may be because older faces are geometric “caricatures” of younger ones. This webpage mentions some work along those lines: 
     
    http://www.utdallas.edu/~otoole/ageing.html 
     
    Something similiar may also explain why the faces of older people may be more difficult to judge in terms of racial or ethnic identity. As the degree of caricature increases, we see more features associated with individual identity rather than group membership. Certainly attractive faces are more difficult to recognize than less attractive ones because they are apparently less of a caricature and have more geometrically average features. This effect may also be noticed when comparing attractive faces across racial and ethnic groups. The more attractive the face, the fewer features it has that are associated with a particular ethnic or racial group. I’m not sure what to say about how the degree of caricature associated with age would interact with attractiveness. Presumably, information regarding age is used to make perceptual judgements of attractiveness that are associated with the highest degrees of fertility. Pre-pubescent faces may be associated with less of a caricature than post-pubescent faces, but they are not sexually attractive.

  24. mort, thanks, that looks interesting.

  25. Maybe it’s my trusting nature (and my imagination) but I do think the brown twin looks like the father, and the white twin resembles the mother.

  26. This is a small bit off-topic, … but I’ve been reading a bit about Europe in 2000 BC to 1000 AD. There are said to have been quite a number of captured fighters sold to the N. Africa area as slaves. 
     
    Anyone know if there is there any phenotypical or genetic evidence that these slaves ever had children?  
     
    No reports of a reverse slave trade, wonder why?

  27. “genetic evidence that these slaves ever had children” 
     
    Maybe they had children with other white slaves. This page 
     
    http://www.townhall.com/opinion/columns/thomassowell/2004/03/24/11163.html 
     
    says that “There were white slaves still being sold in Egypt two decades after blacks were freed in the United States.” Seems a bit hard to believe, but I think Thomas Sowell is pretty reliable.

  28. I’d forgotten about the reports of slavery of whites in Africa 1500-1800. If true, that would probably render moot any remaining genetic influence from 2000 BC to 1000 AD. 
     
    But in either case, are there communities of indigenous whites in N. Africa anywhere? I doubt it, because I believe we would know about it if there were. So where did they go? Were they killed, or did they immigrate back to Europe? Or did they assimilate, in which case there should be some occasional blue eyes or blond hair, I suppose.

  29.  
    But in either case, are there communities of indigenous whites in N. Africa anywhere?
     
     
    the indigenous phenotype has long intersected with that of at southern europeans. why would they remain endogamous anyway? the slaves were converted to islam or their children were raised as muslims in the harem. i don’t think there is a strong haplotype signature though.

  30. I remember a pair of dizygotous twins from high school, Lynn and Suzie. Lynn looked very white, Suzie looked very Arabic – but they had the exact same voice. Not just the same accent, but the same voice, such that you couldn’t tell which one was speaking unless you looked.

  31. “Or did they assimilate, in which case there should be some occasional blue eyes or blond hair, I suppose.” 
     
    I’ve been told by a Frenchman of North African descent that light eyes and/or blonde hair are not uncommon in Algeria.

  32. Bull! 
     
    Sombody needs to call Maury Polvitch for a paternity test. I think they got the sperms mixed up while they were creating these babies in the dish. In America where many African Americans are so white you don’t know their black until they tell you, you cant tell me those two in the picture gave birth to a white baby.

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  34. Well all of you who think that it is not possible for these two to have a white baby, you are wrong. I have son with a black man and our son has blond hair (with my texture), blue eyes, and white skin. God creates children to be all different kinds.

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